This invention relates to the field of electromagnetic radiation and, more particularly, to using a plurality of parallel, uniformly spaced dielectric plates to reflect and conceivably guide high-intensity, monochromatic electromagnetic radiation of any wavelength.
Reflectors of electromagnetic radiation are conventionally made of metals or dielectric materials. Metal reflectors may have reflection efficiencies as high as 98%, but their efficiency is limited by possessing a finite electrical conductivity. High intensity incident radiation (measured in watts per unit area) is partially absorbed by generating an electric current in a thin layer at the surface of the metal, which, in turn, dissipates by generating heat. Such heating causes thermal expansion of the metal medium, as manifested by surface bulges, with consequent distortion of the reflected beam. Another limitation inherent to metal reflectors is that their reflectivity is highly wavelength dependent. Thus, any given metal reflector is most efficient over a fixed wavelength band and its efficiency is substantially lower outside of this band.
The surface of a dielectric material lying adjacent to air, or the interface between two abutting different dielectrics, may also reflect electromagnetic radiation. However, much of the incident radiation is transmitted through this surface or interface unless the reflection mechanism is by total internal reflection (“TIR”). TIR occurs when the incident medium has a higher refractive index that that of the transmitting beam, and the angle subtended by the incident radiation and the normal to the surface is larger than the arcsine function of the ratio of the refractive index of the transmitting medium to the refractive index of the incident medium. This principle explains the efficient transmission of light by optical fibers. TIR cannot occur if the incident medium has a refractive index less than that of the dielectric, as is generally the case when the former is air.
According to a third technology, the deposition on a solid substrate material of multiple layers of different materials having properly chosen refractive indexes and thicknesses can result in, roughly speaking, the realization of a phase relationship, i.e., interference, among reflections from consecutive layers, such that a broad range of transmission and reflection properties may be engineered. For example, such a device could be designed to reflect or transmit only frequencies below or above a certain value, or only within a narrow band (referred to as low-pass, high-pass or band-pass filters, respectively). However, this technology is ill-suited for high-intensity radiation because the radiation field not only penetrates deeply within the layered structure, but, due to multiple internal reflections, tends to build-up field intensities within some of the layers that may be even higher than that of the incident beam. Moreover, as metallic films, which have Ohmic loss, are commonly used with dielectric films in this technology, serious thermal problems are encountered even with moderately intense incident radiation.
There is a need in the art for reflecting high-intensity electromagnetic radiation with high efficiency, without creating high radiation intensity within the medium of the reflective apparatus. This invention addresses the foregoing need in the art.